The general field of this invention relates to the controlling of motors for accurate discrete remote positioning control throughout the range of a mechanical mechanism.
There are many production processes that require frequent adjustments by an operator at the beginning of each new job and during the running of the job. In many instances the adjusting mechanisms are located remotely, requiring the operator to climb a latter or walk a good distance each time an adjustment is necessary.
A good example of such an application is in the printing of newspapers. With the advent of four color process printing, which virtually every newspaper offers today, a popular printing machine called a printing tower has emerged as the chosen printing press configuration. The printing tower consists of two four color printing units arranged vertically so that the four process colors (yellow, magenta, cyan and black) are printed simultaneously on each side of the paper. Each printing unit employs two mechanical mechanisms with hand wheels that are used to make adjustments in registration of each color to the other colors. One hand wheel is used for adjustment in the lateral register, in the X direction, while the other mechanical mechanism provides adjustment in the circumferential register, in the Y direction. Thus a tower has a total of 16 mechanical mechanisms that the operator must manually adjust to make corrections in lateral and circumferential registration of the eight colors that are printed on both sides of the paper.
The tower configuration is considered to be superior, as it requires minimal floor space which is ideal for crowded press rooms, the vertical configuration requires the operator to climb a ladder to reach some of the mechanical mechanisms each time he needs to make an adjustment.
Electric motors have been installed on some of these towers with the intent of providing the operator with remote control capability thus making register adjustments much easier.
In those instances where motors have been added to existing mechanisms a number of deficiencies have still arisen that greatly inhibit the success of motorization due to the great frustration of operation personal when using the motor as a means of introducing register correction as opposed to using the hand wheel.
Some of these deficiencies are related all can be eliminated with the teachings of this disclosure.
The standard method for replacing the hand wheels with a motor includes two operator push buttons, one applying voltage to the motor when depressed by the operator driving the motor in one direction, with the other switch when depressed by the operator driving the motor in the opposite direction. Thus the amount of correction introduced depends upon the direction of correction and for how long the operator depressed the switch. The resolution or minimum correction introduced is limited to the minimum time that the operator could depress the switch which is about one third of a second. There has always been the problem that the maximum slew speed is limited to the resolution required to achieve the accuracy that was desired. Typically a 0.005 inch resolution would yield a slew speed of about 1 inch per minute. If the application was on a full range mechanism requiring moving the mechanism 20 inches for different jobs, than it would take 20 minutes or more to reposition the mechanism. For many applications it is not acceptable to require a two motor system where one motor would be used for obtaining the resolution and another motor used to provide a fast slew speed.
The teaching of this application includes a means of increasing the maximum rate of correction significantly as required while simultaneously increasing the resolution.
Other deficiencies have arisen when replacing the hand wheel. For example, when using the hand wheel the operator can automatically compensate for backlash in the mechanism when making an adjustment. As he turns the hand wheel to make an adjustment, he can feel the lesser pressure required when moving through the backlash and would always move through the backlash and then make his correction when he felt the higher pressure required to move the mechanism. When moving the mechanism using the electric motors, there was no way to sense backlash with several repeated adjustment required to get through the backlash before an actual correction was made. The lack of backlash compensation using the motors caused great difficulty in accurate positioning and significant frustration for the operator.
Hand wheels also have a visual centering means that allows the operator to center each mechanism before starting a new job to make sure that the full range of the mechanism was available if needed to compensate for register errors. Motors have no similar natural centering means with the result that frequently one or more mechanisms would run to a limit stop, requiring a great deal of waste in manually moving all four colors to provide for more range on the unit that ran to the stop.
When using the hand wheel in making a correction, the operator could make an exact and repeatable adjustment in either direction which is not possible when using the motor in the face of backlash.
Until now the only means of overcoming these limitations when using motors for remote positioning of registration has been to add feedback from the printed image using an automatic register control. The automatic register control would eventually correct for any error including when moving through the backlash by making a number of corrections. However automatic register controls have a number of major disadvantages including very high cost, complexity, the need for significant operator training and the difficulty of locating the printed marks that must be included in the art work for the system to operate.
This patent relates to a method to overcome all of these disadvantages and addition provides a low cost alternative to automatic register controls.